Download Chemistry of METALS

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a)Introduction to metals
The rationale of studying metals cannot be emphasized.Since ages, the world over, metals
like gold and silver have been used for commercial purposes.
The periodicity of alkali and alkaline earth metals was discussed in year 2 of secondary
school education. This topic generally deals with:
(a)Natural occurrence of the chief ores of the most useful metals for industrial
/commercial purposes.
(b)Extraction of these metals from their ores for industrial/ commercial purposes.
(c)industrial/ commercial uses of these metals.
(d)main physical and chemical properties /characteristic of the metals.
The metals given detailed emphasis here are; Sodium, Aluminium, Iron, Zinc, Lead
and Copper.
The main criteria used in extraction of metals is based on its position in the
electrochemical/reactivity series and its occurrence on the earth’s crust.
Position on the earth’s crust
If deep on the earth’s crust
deep mining is used
If near the surface ,open
cast mining / quarrying is
used
If the ore is low grade oil, water, and air
is blown forming a froth(froth flotation)
to concentrate
Electrolysis of the ore is used for
reactive metals; Potassium, Sodium,
Magnesium, Calcium, Aluminium
The ore first roasted if it is a carbonate or
sulphide of Zinc, Iron, Tin, Lead, and Copper
to form the oxide
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The oxide is reduced using carbon/ carbon(II)
oxide in a furnace if it is made of Zinc ,Tin,
Lead ,Copper and Iron
1.SODIUM
a) Natural occurrence
Sodium naturally occurs as:
(i)Brine-a concentrated solution of sodium chloride(NaCl(aq)) in salty
seas and oceans.
(ii)Rock salt-solid sodium chloride(NaCl(s)
(iii)Trona-sodium sesquicarbonate(NaHCO3.Na2CO3.2H2O) especially
in lake Magadi in Kenya.
(iv)Chile saltpeter-sodium nitrate(NaNO3)
b)(i)
Extraction of Sodium from brine/Manufacture of Sodium hydroxide/The
flowing mercury cathode cell/ TheCaster-Keller process
I.Raw materials
(i) Brine-concentrated solution of sodium chloride (NaCl (aq))
from salty seas and oceans.
(ii)Mercury
(iii)Water from river/lakes
II. Chemical processes
Salty lakes, seas and oceans contain large amount of dissolved sodium
chloride (NaCl (aq)) solution.
This solution is concentrated to form brine which is fed into an electrolytic
chamber made of suspended Carbon graphite/titanium as the anode and a
continuous flow of Mercury as the cathode.Note
Mercury is the only naturally occurring known liquid metal at room
temperature and pressure
Questions
I. Write the equation for the decomposition of the electrolyte during the
electrolytic process.
H2O(l)
H+(aq)
+
OH-(aq)
NaCl(aq)
Na+(aq) +
Cl-(aq)
II. Name the ions present in brine that moves to the:
(i)Mercury cathode; H+(aq) , Na+(aq)
(ii)Titanium/graphite; OH-(aq), Cl-(aq)
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III. Write the equation for the reaction that take place during the electrolytic
process at the;
Cathode; 2Na+(aq) +
2e
2Na(s)
Anode;
2Cl (aq)
Cl2(g) + 2e
Note
(i)Concentration of 2Cl-(aq) ions is higher than OH- ions causing overvoltage
thus blocking OH- ions from being discharged at the anode.
(ii)Concentration of Na+(aq) ions is higher than H+ ions causing overvoltage
thus blocking H+ ions from being discharged at the cathode.
IV. Name the products of electrolysis in the flowing mercury-cathode cell.
(i)Mercury cathode; Sodium metal as grey soft metal/solid
(ii)Titanium/graphite; Chlorine gas as a pale green gas that turns
moist blue/red litmus papers red then bleaches both. Chlorine gas is
a very useful by-product in;
(i)making (PVC)polyvinylchloride(polychloroethene) pipes.
(ii)chlorination/sterilization of water to kill germs.
(iii)bleaching agent
(iv)manufacture of hydrochloric acid.
Sodium produced at the cathode immediately reacts with the mercury at the
cathode forming sodium amalgam(NaHg) liquid that flow out of the
chamber.
Na(s) + Hg(l)
Na Hg (l)
Sodium amalgam is added distilled water and reacts to form sodium
hydroxide solution, free mercury and Hydrogen gas.
2Na Hg (l) + 2H2O(l)
2NaOH (aq) + 2Hg(l) + H2(g)
Hydrogen gas is a very useful by-product in;
(i)making ammonia gas in the Haber process
(ii)manufacture of hydrochloric acid
(iii)in weather balloons to forecast weather
(iv)as rocket fuel
As the electrolysis of brine continues, the concentration of Cl-ions decreases
and oxygen gas start being liberated. Continuous feeding of the electrolyte is
therefore very necessary.
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III.Uses of sodium hydroxide
The sodium hydroxide produced is very pure and is used mainly in:
(i)Making soapy and soapless detergents.
(ii)making cellulose acetate/rayon
IV. Diagram showing the Manufacture of Sodium hydroxide from the
flowing Mercury-cathode cell.
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V. Environmental effects of Manufacture of Sodium hydroxide from the
flowing Mercury-cathode cell.
1.Most of the Mercury used at the cathode is recycled ;
(i)to reduce the cost because mercury is expensive
(ii)to reduce pollution because mercury kills marine life.
(iii)because it causes chromosomal/genetic mutation to human beings.
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2.Chlorine produced at the anode;
(i)has a pungent irritating smell that causes headache to human beings.
(ii)bleaches any wet substance.
(iii)dissolves water to form both hydrochloric acid and chloric(I)acid
Both cause marine pollution and stomach upsets.
b)(ii)
Extraction of sodium from rock salt/The Downs cell/process
I. Raw materials
(i)Rock salt/solid sodium chloride
(ii)calcium(II)chloride
II. Chemical processes.
Rock salt/ solid sodium chloride is heated to molten state in a chamber lined
with fire bricks on the outside.
Sodium chloride has a melting point of about 800oC. A little calcium (II)
chloride is added to lower the melting point of the electrolyte to about 600oC.
The molten electrolyte is the electrolyzed in a carbon graphite anode
suspended at the centre and surrounded by steel cathode.
Questions
I. Write the equation for the decomposition of the electrolyte during the
electrolytic process.
NaCl(l)
Na+(l)
+
Cl-(l)
Note: In absence of water, the ions are in liquid state.
II. Name the ions present in molten rock salt that move to the;
(i)Steel cathode -Na+(l)
(ii)Carbon graphite anode- Cl-(l)
III. Write the equation for the reaction that take place during the electrolytic
process at the;
(i)Steel cathode
2Na+(l) +
2e
2Na(l)
(ii)Carbon graphite anode
2Cl-(l)
Cl2(g) + 2e
IV. Name the products of electrolysis in the Downs cell at;
(i)Cathode:
Grey solid Sodium metal is less dense than the molten electrolyte
and therefore float on top of the cathode to be periodically tapped off.
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(ii)Anode:
Pale green chlorine gas that turns moist/damp/wet blue/red litmus papers
red then bleaches/decolorizes both. Chlorine gas is again a very useful
by-product in;
(i)making (PVC)polyvinylchloride(polychloroethene) pipes.
(ii)chlorination/sterilization of water to kill germs.
(iii)bleaching agent
(iv)manufacture of hydrochloric acid.
A steel diaphragm/gauze is suspended between the electrodes to prevent
recombination of sodium at the cathode and chlorine gas at the anode back
to sodium chloride.
III. Diagram showing the Downs cell/process for extraction of sodium
IV. Uses of sodium.
1.Sodium vapour is used as sodium lamps to give a yellow light in street
lighting.
2.Sodium is used in making very useful sodium compounds like;
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(i)Sodium hydroxide(NaOH)
(ii)Sodium cyanide(NaCN)
(iii)Sodium peroxide(Na2O2)
(iv)Sodamide(NaNH2)
3.An alloy of Potassium and Sodium is used as coolant in nuclear reactors.
V. Environmental effects of Downs cell.
1.Chlorine produced at the anode;
(i)has a pungent irritating smell that causes headache to human beings.
(ii)bleaches any wet substance.
(iii)dissolves water to form both hydrochloric acid and chloric(I)acid
Both cause marine pollution and stomach upsets.
2.Sodium metal rapidly react with traces of water to form alkaline Sodium
hydroxide(NaOH(aq))solution. This raises the pH of rivers/lakes killing
aquatic lifein case of leakages.
VI. Test for presence of Na.
If a compound has Na+ ions in solid/molten/aqueous state then it changes a
non-luminous clear/colourless flame to a yellow coloration but does not burn
Experiment
Scoop a portion of sodium chloride crystals/solution in a clean metallic
spatula. Introduce it to a clear /colourless Bunsen flame.
Observation
Yellow coloration
Inference
Na+
Practice
(i)Calculate the time taken in hours for 230kg of sodium to be produced
in the Downs cell when a current of 120kA is used.
(ii)Determine the volume of chlorine released to the atmosphere.
(Na=23.0),Faraday constant=96500C.I mole of a gas =24dm3 at r.t.p)
Working:
Equation at the cathode:
2Na+ (l) + 2e -> 2Na(l)
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2 mole of electrons = 2 Faradays = 2 x 96500 C deposits a mass = molar mass
of Na = 23.0g thus;
23.0 g
-> 2 x 96500 C
(230 x 1000)g ->
230 x 1000 x 2 x 96500
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= 1,930,000,000 / 1.93 x 10 9C
Time(t) in seconds
= Quantity of electricity
Current(I) in amperes
Substituting
= 1,930,000,000 / 1.93 x 10 9C
120 x 1000A
= 16,083,3333seconds / 268.0556 minutes
= 4.4676hours
Volume of Chlorine
Method 1
Equation at the anode:
2 Cl- (l) -> Cl2(g) + 2e
From the equation:
2 moles of electrons = 2 Faradays =2 x 96500C
2 x 96500C -> 24dm3
1,930,000,000 / 1.93 x 10 9C->1,930,000,000 / 1.93x10 9C x 24
2 x 96500C
Volume of Chlorine = 240,000dm3 /2.4 x 105dm3
Method 2
Equation at the anode:
Cl- (l) -> Cl2(g) + 2e
Mole ratio of products at Cathode: anode = 1:1
Moles of sodium at cathode =(230 x 1000 )g= 10,000moles
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10,000moles of Na =
10,000moles moles of Chlorine
1 moles of Chlorine gas = 24000cm3
10,000moles of Chlorine- > 10000 x 24
=240,000dm3 / 2.4x 105dm3
Method 3
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Equation at the anode: Cl- (l) -> Cl2(g) + 2e
Ratio of Faradays of products at Cathode: anode = 2:2
=> 2 x 96500C produce 24000cm3 of chlorine gas Then: 1,930,000,000 /
1.93 x 10 9C ->
1,930,000,000 / 1.93 x 10 9C x24 = 240,000dm3
2 x 96500
(iij)The sodium metal produced was reacted with water to form
25000dm3 solution in a Caster-Keller tank.
(a)Calculate the concentration of the resulting solution in moles per litre.
(b)The volume of gaseous products formed at s.t.p(1 mole of gas =22.4
dm3 at s.t.p)
Chemical equation at Caster-Keller tank
2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2 (g)
Mole ratio Na:NaOH = 2 : 2 => 1:1
Moles Na =10000moles=10000moles of NaOH
25000dm3 ->10000moles of NaOH
1dm3
-> 10000 x 1 = 0.4M / 0.4 moles/dm3
25000
Mole ratio Na: H2 (g) = 2 : 1
Moles Na = 10000moles = 5000moles of H2 (g)
Volume of H2 (g) = moles x molar gas volume at s.t.p
=> 5000moles x 22.4 dm3
=120,000dm3
(iv)The solution formed was further diluted with water for a titration
experiment. 25.0 cm3 of the diluted solution required 20.0cm3 of 0.2M
sulphuric(VI)acid for complete neutralization. Calculate the volume of
water added to the diluted solution before titration.
Chemical equation
2NaOH(aq) + H2SO4(aq) -> Na2SO4(aq) + H2O(l)
Moles ratio NaOH : H2SO4 = 2 : 1
Moles ratio H2SO4 = molarity x volume => 0.2M x 20
1000
1000
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=4.0 x 10-3 moles
Moles NaOH = 2 x 4.0 x 10-3 moles= 8.0 x 10-3 moles
Molarity of NaOH= Moles x 1000=> 8.0 x 10-3 moles x 1000
volume
25
-3
=0.16 molesdm /M
Volume used during dilution
C1V1 = C2V2 => 0.4M x V1 = 0.16 M x 25
= 0.16 M x 25 = 10cm3
0.4
(a) Below is a simplified diagram of the Downs Cell used for the
manufacture of sodium. Study it and answer the questions that follow
(i)What material is the anode made of? Give a reason (2 mks)
Carbon graphite/Titanium
This because they are cheap and inert/do not influence/affect the products
of electrolysis
(ii) What precaution is taken to prevent chlorine and sodium from recombination? ( 1 mks)
Using a steel gauze/diaphragm separating the cathode from anode
(iii) Write an ionic equation for the reaction in which chlorine gas is
formed ( 1mk)
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2Cl-(l)
->
Cl2(g)
+
2e
(b) In the Downs process, (used for manufacture of sodium), a certain
salt is added to lower the melting point of sodium chloride from about
8000C to about 6000C.
(i) Name the salt that is added
(1mk)
Calcium chloride
(ii) State why it is necessary to lower the temperature(1mk)
To reduce the cost of production
(c) Explain why aqueous sodium chloride is not suitable as an electrolyte
for the manufacture of sodium in the Downs process( 2mk)
The sodium produced react explosively/vigorously with water in the aqueous
sodium chloride
(d) Sodium metal reacts with air to form two oxide. Give the formulae of
two oxides( 1mk)
Na2O Sodium oxide(in limited air)
Na2O2 Sodium peroxide(in excess air)
2.ALUMINIUM
a)Natural occurrence
Aluminium is the most common naturally occurring metal. It makes 7% of the
earths crust as:
(i)Bauxite ore- Hydrated aluminium oxide(Al2O3.2H2O)
(ii)Mica ore-Potassium aluminium silicate(K2Al2Si6O16)
(iii)China clay ore- aluminium silicate (Al2Si6O16)
(iv)Corrundum-Anhydrous aluminium oxide(Al2O3)
b)Extraction of aluminium from Bauxite/Halls cell/process)
The main ore from which aluminium is extracted is Bauxite ore- hydrated
aluminium oxide(Al2O3.2H2O).
The ore is mined by open-caste mining method/quarrying where it is scooped
together with silica/sand/silicon(IV)oxide (SiO2) and soil/ iron(III)oxide
(Fe2O3) as impurities.
The mixture is first dissolved in hot concentrated sodium/potassium hydroxide
solution.
The alkalis dissolve both bauxite and silicon(IV)oxide.
This is because bauxite is amphotellic while silicon(IV)oxide is acidic.
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Iron(III)oxide (Fe2O3) is filtered of /removed as a residue.
Carbon(IV)oxide is bubbled into the filtrate to precipitate aluminium (III)
hydroxide (Al(OH)3) as residue.
The aluminium (III) hydroxide (Al(OH)3) residue is filtered off. Silicon
(IV)oxide remain in the solution as filtrate. Aluminium (III) hydroxide
(Al(OH)3) residue is then heated to form pure aluminium (III)oxide(Al2O3)
2Al(OH)3 (s)
Al2O3 (s) + 3H2O(l)
Pure aluminium (III)oxide (Al2O3) has a very high melting point of 2015oC.
Alot of energy is required to melt the oxide.
It is therefore dissolved first in molten cryolite /sodium hexafluoroaluminate
(III)/Na3AlF6 to lower the melting point to about 800oC.
The molten electrolyte is put in the Hall cell made up of a steel tank lined with
carbon graphite and an anode suspended into the electrolyte.
During the electrolysis:
(i)At the cathode;
4Al3+(l) + 12e
(ii) At the anode;
6O2-(l)
4Al(l)
3O2(g)
+ 12e
Aluminium is denser than the electrolyte therefore sink to the bottom of the
Hall cell.
At this temperature ,the Oxygen evolved/produced at the anode reacts with
carbon anode to form carbon(IV)oxide gas that escape to the atmosphere.
C(s) + O2(g)
CO2(g)
The anode thus should be continuously replaced from time to time.
Flow chart summary of extraction of aluminium from Bauxite
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Hot concentrated sodium
hydroxide
Bauxite(Al2O3.2H2O) ore with
impurities Fe2O3 and SiO2
Crush (increase
surface area)
Powdered mixture
Sodium aluminate (NaAl(OH)4)
Carbon(IV)oxide
and sodium silicate (Na2SiO3)
as filtrate
Aluminium hydroxide
(Al(OH)3) as residue
Roast at
1000oC
Iron(III)oxide- Fe2O3 as
residue
Cryolite
Sodium silicate (Na2SiO3)
Aluminium
(III) Oxide
Electrolysis
Pure aluminium
sinks in Hall cell
Oxygen gas at anode
c) Diagram showing the Hall cell / process for extraction of Bauxite
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d)Uses of aluminium
(i) In making aeroplane parts, buses, tankers, furniture because aluminium is
very light.
(ii)Making duralumin-an alloy which is harder and has a higher tensile
strength
(iii)Making utensils,sauce pans,spoons because it is light and good conductor
of electricity.
(iv)Making overhead electric cables because it is light,ductile and good
conductor of electricity.
(iv)Used in the thermite process for production of Manganese, Chromium
amd Titanium.
e) Environmental effects of extracting aluminium from Bauxite.
Carbon(IV)oxide gas that escape to the atmosphere is a green house gas that
causes global warming.
Bauxite is extracted by open caste mining that causes soil/environmental
degradation.
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f) Test for presence of Al3+
If an ore is suspected to contain Al3+ it is;
(i)added hot concentrated sulphuric(VI)/Nitric(V)acid to free the ions
present.
(ii)the free ions are then added a precipitating reagent like 2M sodium
hydroxide /2M aqueous ammonia.
Observation
White precipitate in excess 2M NaOH(aq)
White precipitate in excess 2M NH3(aq)
No black precipitate on adding Na2S(aq)
No white precipitate on adding either
NaCl(aq),HCl(aq),H2SO4(aq),Na2SO4(aq)
Inference
Pb2+ , Al3+, Zn2+
Pb2+ , Al3+
Al3+
Al3+
Practice
1.An unknown rock X was discovered in Ukraine. Test with dilute sulphuric (VI)acid
shows rapid effervescence with production of a colourless gas A that forms a white
precipitate with lime water and colourless solution B. On adding 3cm3 of 2M sodium
hydroxide, a white precipitate C is formed that dissolves to form a colourless solution D
on adding more sodium hydroxide. On adding 2M aqueous ammonia, a white precipitate
E is formed which persist in excess aqueous ammonia.On which on adding 5cm3 of 1M
Lead(II)nitrate(V) to F a white precipitate G is formed which remains on heating.
Identify:
A
Hydrogen/H2
B
Aluminium sulphate(VI)/Al2(SO4) 3
C
Aluminium hydroxide/ Al(OH4) 3
D
Tetrahydroxoaluminate(III)/ [Al(OH4) 3] E
Aluminium hydroxide/ Al(OH) 3
F
Aluminium chloride/ AlCl3
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2.Aluminium is obtained from the ore with the formula Al2O3. 2H2O. The ore is first
heated and refined to obtain pure aluminium oxide (Al2O3). The oxide is then
electrolysed to get Aluminium and oxygen gas using carbon anodes and carbon as
cathode. Give the common name of the ore from where aluminium is extracted from ½
mark
What would be the importance of heating the ore first before refining it?1 mark
To remove the water of crystallization
The refined ore has to be dissolved in cryolite first before electrolysis. Why is this
necessary? 1½ mark
To lower the melting point of aluminium oxide from about 2015oC to 900oC so as to
lower /reduce cost of production
Why are the carbon anodes replaced every now and then in the cell for electrolysing
aluminium oxide?
1 mark
Oxygen produced at anode react with carbon to form carbon(IV)oxide gas that
escape
State two uses of aluminium
In making aeroplane parts, buses, tankers, utensils, sauce pans,spoons
Making overhead electric cables
Making duralumin
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3. IRON
a)Natural occurrence
Iron is the second most common naturally occurring metal. It makes 4% of the
earths crust as:
(i)Haematite(Fe2O3)
(ii)Magnetite(Fe3O4)
(iii)Siderite(FeCO3)
b)The blast furnace for extraction of iron from Haematite and Magnetite
a)Raw materials:
(i)Haematite(Fe2O3)
(ii)Magnetite(Fe3O4)
(iii)Siderite(FeCO3)
(iv)Coke/charcoal/ carbon
(v)Limestone
b)Chemical processes:
Iron is usually extracted from Haematite (Fe2O3), Magnetite(Fe3O4) Siderite
(FeCO3).These ores contain silicon(IV)oxide(SiO2) and aluminium(III)oxide
(Al2O3) as impurities.
When extracted from siderite, the ore must first be roasted in air to decompose
the iron(II)Carbonate to Iron(II)oxide with production of carbon(IV)oxide gas:
FeCO3(s)
FeO(s)
+
CO2(g)
Iron(II)oxide is then rapidly oxidized by air to iron(III)oxide(Haematite).
4FeO(s)
+
O2(g)
2Fe2O3(s)
Haematite (Fe2O3), Magnetite(Fe3O4), coke and limestone are all then fed
from top into a tall (about 30metres in height) tapered steel chamber lined
with refractory bricks called a blast furnace.
The furnace is covered with inverted double cap to prevent/reduce amount of
any gases escaping .
Near the base/bottom, blast of hot air at about 1000K (827oC) is driven/forced
into the furnace through small holes called Tuyeres.
As the air enters ,it reacts with coke/charcoal/carbon to form carbon(IV)oxide
gas. This reaction is highly exothermic.
CO2 (g) ∆H = -394kJ
C(s)+ O2(g)
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This raises the temperature at the bottom of the furnace to about
2000K(1650oC).As Carbon(IV)oxide gas rises up the furnace it reacts with
more coke to form carbon(II)oxide gas.This reaction is endothermic.
2CO (g) ∆H = +173kJ
CO2 (g) + C(s)
Carbon(II)oxide gas is a strong reducing agent that reduces the ores at the
upper parts of the furnace where temperatures are about 750K(500oC) i.e.
For Haematite;
Fe2O3 (s) +
3CO(g)
2Fe(s) + CO2(g)
For Magnetite;
Fe3O4 (s) +
4CO(g)
3Fe(s) + 4CO2(g)
Iron is denser than iron ore. As it falls to the hotter base of the furnace it
melts and can easily be tapped off.
Limestone fed into the furnace decomposes to quicklime/calcium oxide and
produce more carbon(IV)oxide gas.
CaCO3(s)
CaO(s) + CO2(g)
Quicklime/calcium oxide reacts with the impurities silicon(IV)oxide(SiO2)
and aluminium(III)oxide(Al2O3)in the ore to form calcium silicate and
calcium aluminate.
CaO(s) + SiO2(s)
CaO(s) + Al2O3(s)
CaSiO3 (l)
Ca Al2O4 (l)
Calcium silicate and calcium aluminate mixture is called slag.Slag is denser
than iron ore but less dense than iron therefore float on the pure iron. It is
tapped at different levels to be tapped off for use in:
(i)tarmacing roads
(ii) cement manufacture
(iii)as building construction material
(c)Uses of Iron
Iron obtained from the blast furnace is hard and brittle. It is called Pig iron. It
is remelted, added scrap steel then cooled. This iron is called cast iron.
Iron is mainly used to make:
(i)gates ,pipes, engine blocks, rails, charcoal iron boxes,lamp posts because it
is cheap.
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(ii)nails, cutlery, scissors, sinks, vats, spanners,steel rods, and railway points
from steel.
Steel is an alloy of iron with carbon, and/or Vanadium, Manganese, Tungsten,
Nickel ,Chromium. It does not rust/corrode like iron.
e) Environmental effects of extracting Iron from Blast furnace
(i)Carbon(IV)oxide(CO2) gas is a green house gas that causes/increases global
warming if allowed to escape/leak from the furnace.
(ii)Carbon(II)oxide(CO)gas is a highly poisonous/toxic odourless gas that can
kill on leakage.
It is preferentially absorbed by the haemoglobin in mammals instead of
Oxygen to form a stable compound that reduce free hemoglobin in the blood.
(iii) Haematite (Fe2O3), Magnetite(Fe3O4) and Siderite (FeCO3) are extracted
through quarrying /open cast mining that cause soil / environmental
degradation .
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f) Test for the presence of Iron
Iron naturally exist in its compound as Fe2+ /Fe3+
If an ore is suspected to contain Fe2+ /Fe3+ it is;
(i)added hot concentrated sulphuric(VI)/Nitric(V)acid to free the ions
present.
(ii)the free ions are then added a precipitating reagent like 2M sodium
hydroxide /2M aqueous ammonia which forms;
I) an insoluble green precipitate in excess of 2M sodium hydroxide
/2M aqueous ammonia if Fe2+ ions are present.
I) an insoluble brown precipitate in excess of 2M sodium
hydroxide /2M aqueous ammonia if Fe2+ ions are present.
Observation
green precipitate in excess 2M NaOH(aq)
green precipitate in excess 2M NH3(aq)
brown precipitate in excess 2M NaOH(aq)
brown precipitate in excess 2M NH3(aq)
Practice questions
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Inference
Fe2+
Fe2+
Fe3+
Fe3+
4.COPPER
a)Natural occurrence
Copper is found as uncombined element/metal on the earths crust in Zambia,
Tanzania, USA and Canada .The chief ores of copper are:
(i)Copper pyrites(CuFeS2)
(ii)Malachite(CuCO3.Cu(OH)2)
(iii)Cuprite(Cu2O)
b)Extraction of copper from copper pyrites.
Copper pyrites are first crushed into fine powder. The powdered ore is the
added water and oil. The purpose of water is to dissolve hydrophilic
substances/particle. The purpose of oil is to make cover copper ore particle so
as to make it hydrophobic
Air is blown through the mixture. Air creates bubbles that stick around
hydrophobic copper ore. The air bubbles raise through buoyancy small
hydrophobic copper ore particles to the surface. A concentrated ore floats at
the top as froth. This is called froth flotation. The concentrated ore is then
skimmed off.The ore is then roasted in air to form copper(I)sulphide
,sulphur(IV)oxide and iron (II) oxide.
2CuFeS2(s) + 4O2(g)
Cu2S(s) + 3SO2(g) + 2FeO(s)
Limestone (CaCO3) and silicon(IV)oxide (SiO2) are added and the mixture
heated in absence of air.Silicon(IV)oxide (SiO2) reacts with iron (II) oxide to
form Iron silicate which constitutes the slag and is removed.
FeO(s) + SiO2(s)
FeSiO3(s)
The slag separates off from the copper(I)sulphide. Copper(I)sulphide is then
heated in a regulated supply of air where some of it is converted to copper (I)
oxide.
2Cu2S (s) + 3O2(g)
2Cu2S(s) + 2SO2(g)
The mixture then undergo self reduction in which copper(I)oxide is reduced
by copper(I)sulphide to copper metal.
Cu2S (s) + 2Cu2O (s)
6Cu (s) + SO2(g)
The copper obtained has Iron, sulphur and traces of silver and gold as
impurities.It is therefore about 97.5% pure. It is refined by
electrolysis/electrolytic method.
During the electrolysis of refining copper, the impure copper is made the
anode and a small pure strip is made the cathode.
Electrode ionization takes place where:
At the anode;
22
Cu(s)
Cu2+ (aq) + 2e
Note: Impure copper anode dissolves/erodes into solution and decreases in
size.
At the Cathode;
Cu2+ (aq) + 2e
Cu(s)
Note: The copper ions in the electrolyte(CuSO4) are reduced and deposited as
copper metal at the cathode. The copper obtained is 99.98% pure.
Valuable traces of silver and gold collect at the bottom of the electrolytic cell
as sludge. It is used to finance the extraction of copper pyrites.
(c)Flow chart summary of extraction of copper from Copper pyrites
Water
Copper pyrites(CuFeS2) ore with
impurities Fe2O3 and SiO2
Crush (increase
surface area)
Froth
flotation
Excess air
Silicon(IV)
oxide
Rocky impurities
1st roasting chamber
Limestone
Oil
Concentration
chamber
Cu2S
Sulphur(IV)Oxide
Smelting furnace
Limited air
Calcium
aluminate
(CaAl2O4)slag
Iron Silicate
(FeSiO3)Slag
Cu2S, Cu2O
Impure copper
2nd roasting furnace
Self reduction
Sulphur(IV)Oxide
Electrolysis using Copper electrodes
23
Cathode; Pure Copper deposited.
Anode; Impure Copper eroded.
Electrolytic purification of impure copper
d) Uses of copper
Copper is mainly used in:
(i)making low voltage electric cables,contact switches, cockets and plugs
because it is a good conductor of electricity.
(ii)Making solder because it is a good thermal conductor.
(iii)Making useful alloys e.g.
-Brass is an alloy of copper and Zinc(Cu/Zn)
-Bronze is an alloy of copper and Tin(Cu/Sn)
-German silver is an alloy of copper ,Zinc and Nickel(Cu/Zn/Ni)
(iv)Making coins and ornaments.
e) Environmental effects of extracting copper from Copper pyrites
(i)Sulphur(IV)oxide is a gas that has a pungent poisonous smell that causes
head ache to human in high concentration.
(ii)Sulphur(IV)oxide gas if allowed to escape dissolves in water /rivers/rain to
form weak sulphuric(IV)acid lowering the pH of the water leading to marine
pollution, accelerated corrosion/rusting of metals/roofs and breathing
problems to human beings.
24
(iii)Copper is extracted by open caste mining leading to land /environmental
/soil degradation.
f) Test for the presence of copper in an ore
Copper naturally exist in its compound as Cu2+ /Cu+
Copper (I) / Cu+ is readily oxidized to copper(II)/ Cu2+
If an ore is suspected to contain Cu2+ /Cu+ it is;
(i)added hot concentrated sulphuric(VI)/Nitric(V)acid to free the ions
present.
(ii)the free ions are then added a precipitating reagent; 2M sodium
hydroxide /2M aqueous ammonia which forms;
I) an insoluble blue precipitate in excess of 2M sodium hydroxide
2+
if Cu ions are present.
I) an insoluble blue precipitate in 2M aqueous ammonia that
dissolve to royal/deep blue solution in excess if Cu2+ ions are present.
Observation
blue precipitate in excess 2M NaOH(aq)
blue precipitate,dissolve to royal/deep blue
solution in excess 2M NH3(aq)
Inference
Cu2+
Cu2+
g)Sample questions
Copper is extracted from copper pyrites as in the flow chart outlined below.
Study it and answer the questions that follow
25
5.ZINC and LEAD
a)Natural occurrence
Zinc occurs mainly as:
(i)Calamine-Zinc carbonate(ZnCO3)
(ii)Zinc blende-Zinc sulphide(ZnS)
Lead occurs mainly as Galena-Lead(II)Sulphide mixed with Zinc blende:
b)Extraction of Zinc/Lead from Calamine ,Zinc blende and Galena.
During extraction of Zinc , the ore is first roasted in air:
For Calamine Zinc carbonate decompose to Zinc oxide and carbon(IV) oxide
gas.
ZnCO3(s)
ZnO(s)
+
CO2(g)
Zinc blende does not decompose but reacts with air to form Zinc oxide and
sulphur(IV) oxide gas.
Galena as a useful impurity also reacts with air to form Lead(II) oxide and
sulphur(IV) oxide gas.
2ZnS(s) + 3O2(g)
(Zinc blende)
2ZnO(s)
+
2SO2(g)
2PbS(s) + 3O2(g)
(Galena)
2PbO(s)
+
2SO2(g)
The oxides are mixed with coke and limestone/Iron(II)oxide/ Aluminium (III)
oxide and heated in a blast furnace.
At the furnace temperatures limestone decomposes to quicklime/CaO and
produce Carbon(IV)oxide gas.
CaCO3(s)
CaO(s) + CO2 (g)
Carbon(IV)oxide gas reacts with more coke to form the Carbon(II)oxide gas.
C(s) + CO2 (g)
2CO (g)
Both Carbon(II)oxide and carbon/coke/carbon are reducing agents.
26
The oxides are reduced to the metals by either coke or carbon (II)oxide.
ZnO(s)
PbO(s)
+
+
C(s)
C(s)
Zn(g) + CO (g)
Pb(l) + CO (g)
PbO(s)
PbO(s)
+
+
CO(s)
CO(s)
Pb(l) + CO2 (g)
Pb(g) + CO2 (g)
At the furnace temperature:
(i)Zinc is a gas/vapour and is collected at the top of the furnace. It is
condensed in a spray of molten lead to prevent reoxidation to Zinc
oxide. On further cooling , Zinc collects on the surface from where it can
be tapped off
(ii)Lead is a liquid and is ale to trickle to the bottom of the furnace from
where it is tapped off.
Quicklime/CaO, Iron(II)Oxide, Aluminium(III)oxide are used to remove
silica/silicon(IV)oxide as silicates which float above Lead preventing its
reoxidation back to Lead(II)Oxide.
CaO(s) + SiO2(s)
CaSiO3(s/l)
(Slag-Calcium silicate)
FeO(s) + SiO2(s)
FeSiO3(s/l)
(Slag-Iron silicate)
Al2O3(s) + SiO2(s)
Al2SiO4(s/l)
(Slag-Aluminium silicate)
c)Flow chart on extraction of Zinc from Calamine ,Zinc blende.
Zinc ore (calamine
/Zinc blende
Powdered ore
Oil
Water
Froth flotation
CO2 from
calamine
SO2 from
Zinc blende
Roasting chamber
Iron/aluminium/ Limestone
Coke
Water
Filtration
Condenser
27
Reduction chamber
Slag (Iron silicate/
aluminium
silicate/calcium
d) Flow chart on extraction of Lead from Galena
Lead ore/Galena
Iron/Limestone
Powdered ore
coke
oil
Water
Froth flotation
Roasting chamber
Reduction chamber
SO2(g)
Slag(Iron silicate)
Filtration
Condenser
LEAD VAPOUR
Zinc residue
e) Uses of Lead
Lead is used in:
(i)making gun-burettes.
(ii)making protective clothes against nuclear (alpha rays/particle)
radiation in a nuclear reactor.
(iii)Mixed with tin(Sn) to make solder alloy
f) Uses of Zinc
Zinc is used in:
28
(i)Galvanization-when iron sheet is dipped in molten Zinc ,a thin layer
of Zinc is formed on the surface.Since Zinc is more reactive than iron ,it reacts
with elements of air(CO2/ O2 / H2O) to form basic Zinc
carbonate(ZnCO3.Zn(OH)2).This sacrificial method protects iron from
corrosion/rusting.
(ii)As negative terminal and casing in dry/Laclanche cells.
(iii)Making brass alloy with copper(Cu/Zn)
g) Environmental effects of extracting Zinc and Lead.
(i) Lead and Lead salts are carcinogenic/causes cancer
(ii)Carbon(IV)oxide is a green house gas that causes/accelerate global
warming.
(iii)Carbon(II)oxide is a colourless odourless poisonous /toxic gas that
combines with haemoglobin in the blood to form stable carboxyhaemoglobin
reducing free haemoglobin leading to death.
(iv) Sulphur(IV)oxide is a gas that has a pungent poisonous smell that causes
headache to human if in high concentration.
(v)Any leakages in Sulphur(IV)oxide gas escapes to the water bodies to form
weak sulphuric(VI)acid lowering the pH of the water. This causes marine
pollution /death of aquatic life, accelerated rusting/corrosion of metals/roofs
and breathing problems to human beings.
h) Test for presence of Zinc/ Lead.
If an ore is suspected to contain Zinc/Lead it is:
I.added hot concentrated Nitric(V)acid to free the ions present.
Note:
Concentrated Sulphuric(VI)acid forms insoluble PbSO4 thus cannot be used
to free the ions in Lead salts.
II.the free ions are then added a precipitating reagent mostly 2M sodium
hydroxide or 2M aqueous ammonia with the formation of;
(i)a soluble precipitate in excess of 2M sodium hydroxide if Zn2+, Pb2+,
Al3+ions are present.
(ii)a white precipitate that dissolves to form a colorless solution in
excess 2M aqueous ammonia if Zn2+ions are present.
(iii)an insoluble white precipitate in excess 2M aqueous ammonia if
Pb2+, Al3+ions are present.
(iv) Pb2+ ions form a white precipitate when any soluble SO42-, SO32-,
CO32-, Cl-, is added while Al3+ ions do not form a white precipitate
29
(v) Pb2+ ions form a yellow precipitate when any soluble I-(e.g.
Potassium/sodium Iodide) is added while Al3+ ions do not form a yellow
precipitate.
(vi) Pb2+ ions form a black precipitate when any soluble S-(e.g.
Potassium/sodium sulphide) is added while Al3+ ions do not form a black
precipitate.i.e;
Observation
White precipitate in excess 2M NaOH (aq)
White precipitate that dissolves to form a
colourless solution in excess 2M NH3(aq)
White precipitate in excess 2M NH3(aq)
White precipitate on adding about 4 drops of
either Na2CO3(aq), Na2SO3(aq), Na2SO4(aq),
H2SO4(aq), HCl(aq), NaCl(aq)
Yellow precipitate on adding about 4 drops of
of KI(aq).NaI (aq)
Black precipitate on adding aout 4 drops of
Na2S(aq)/K2S(aq)
30
Inference
Zn2+, Pb2+, Al3+ ions
Zn2+ ions
Pb2+, Al3+ ions
Pb2+ions
Pb2+ ions
Pb2+ ions
6.GENERAL SUMMARY OF METALS
a) Summary methods of extracting metal from their ore
The main criteria used in extraction of metals is based on its position in the
electrochemical/reactivity series and its occurrence on the earth’s crust.
Position on the earth’s crust
If deep on the earth’s
crust use deep mining
If near the surface use open
cast mining / quarrying
Add oil, water, and blow air to form froth
to concentrate the ore if it is a low grade
Electrolyse the ore if it is made of
reactive metals; Potassium, Sodium,
Magnesium, Calcium, Aluminium
Roast the ore first if it is a
carbonate / sulphide of Zinc,
Iron, Tin, Lead, and copper to
form the oxide
Reduce the oxide using carbon in a
furnace if it is made of Zinc ,Tin,
Lead ,Copper and Iron
31
b) Summary of extraction of common metal.
Metal
Chief
Chemical
Method of extraction
ore/s
formula of
ore
Sodium
Rock salt NaCl(s)
Downs process
Through electrolysis of
molten NaCl (CaCl2
lower m.pt from 800oC->
600oC)
Sodium/
Brine
NaCl(aq)
Flowing mercury
sodium
cathode cell
hydroxide
Through electrolysis of
concentrated NaCl(aq)
Aluminium Bauxite
Al2O3.2H2O Halls process
Through electrolysis of
molten Al2O3. (Cryolite
lower m.pt from 2015oC
-> 800oC)
Iron
Haematite Fe2O3
Magnetite Fe3O4
Blast furnace
Reduction of the ore by
carbon(II)oxide
Main equation during
extraction
Cathode:
2Na+(l) + 2e -> 2Na(l)
Anode:
2Cl-(l) -> Cl2(g) + 2e
Cathode:
2Na+(aq)+2e ->2Na(aq)
Anode:
2Cl-(aq) -> Cl2(g) + 2e
Cathode:
4Al3+(l) + 12e -> 4Al(l)
Anode:
6O2-(l) -> 3O2(g) + 12e
Fe2O3(s)+ 3CO(g)
2Fe(l) +3CO2(g)
Fe3O4(s)+ 4CO(g)
3Fe(l) +4CO2(g)
Copper
Copper
pyrites
CuFeS2
Roasting the ore in air
to get Cu2S.
Heating Cu2S ore in
regulated supply of air.
Reduction of Cu2O by
Cu2S
2CuFeS2 (s)+ 4O2(g) ->
Cu2S(s)+3SO2(g)
+2FeO(s)
2Cu2S (s)+ 3O2(g) ->
2Cu2O(s)+2SO2(g)
Cu2S (s)+ 2Cu2O(s) ->
6Cu(s)+ SO2(g)
Zinc
Calamine
ZnCO3
Roasting the ore in air
to get ZnO
32
ZnCO3(s)-> ZnO(s) +
CO2(g)
Blast furnace
/reduction of the oxide 2ZnS(s) +3O2(g) ->
by
2ZnO(s) + 2SO2(g)
Carbon(II)Oxide/Carbon
ZnO(s) + CO(g)->
Zn(s) + CO2(g)
Lead
Galena
PbS
Blast furnaceReduction of the oxide
by carbon(II)oxide
/Carbon
c) Common alloys of metal.
Alloy name
Constituents of the alloy
Brass
Copper and Zinc
Bronze
Copper and Tin
Soldier
Lead and Tin
Duralumin
Aluminium, Copper and
Magnesium
Steel
Nichrome
Iron, Carbon ,Manganese
and other metals
Nichrome and Chromium
German silver
Copper,Zinc and Nickel
PbO(s) + CO(g)->
Pb(s) + CO2(g)
Uses of the alloy
Making scews and bulb caps
Making clock springs,electrical contacts
and copper coins
Soldering, joining electrical contacts
because of its low melting points and high
thermal conductivity
Making aircraft , utensils ,windows frames
because of its light weight and corrosion
resistant.
Railway lines , car bodies girders and
utensils.
Provide resistance in electric heaters and
ovens
Making coins
d) Physical properties of metal.
Metals form giant metallic structure joined by metallic bond from electrostatic attraction
between the metallic cation and free delocalized electrons.
This makes metals to have the following physical properties:
(i)High melting and boiling points
The giant metallic structure has a very close packed metallic lattice joined by strong
electrostatic attraction between the metallic cation and free delocalized electrons.The
more delocalized electrons the higher the melting/boiling points e.g.
Aluminium has a melting point of about 2015oC while that of sodium is about 98oC.This
is mainly because aluminium has more/three delocalized electrons than sodium/has one.
Aluminium has a boiling point of about 2470oC while that of sodium is about 890oC.This
is mainly because aluminium has more/three delocalized electrons than sodium/has one.
33
(ii)High thermal and electrical conductivity
All metals are good thermal and electrical conductors as liquid or solids. The more
delocalized electrons the higher the thermal and electrical conductivity. e.g.
Aluminium has an electrical conductivity of about 3.82 x 19-9 ohms per metre. Sodium
has an electrical conductivity of about 2.18 x 19-9 ohms per metre.
(iii)Shiny/Lustrous
The free delocalized electrons on the surface of the metal absorb, vibrate and then
scatter/re-emit/lose light energy. All metals are therefore usually shades of grey in colour
except copper which is shiny brown.e.g.
Zinc is bluish grey while iron is silvery grey.
(iv)High tensile strength
The free delocalized electrons on the surface of the metal atoms binds the surface
immediately when the metal is coiled/folded preventing it from breaking /being brittle.
(v)Malleable.
Metals can be made into thin sheet. The metallic crystal lattice on being
beaten/pressed/hammered on two sides extend its length and width/bredth and is then
immediately bound by the delocalized electrons preventing it from breaking/being brittle.
(vi)Ductile.
Metals can be made into thin wires. The metallic crystal lattice on being
beaten/pressed/hammered on all sides extend its length is then immediately bound by the
delocalized electrons preventing it from breaking/being brittle.
Revision questions
1.Given some soil , dilute sulphuric(VI)acid,mortar,pestle,filter paper,filter funnel
and 2M aqueous ammonia,describe with explanation,how you would show that the
soil contain Zinc.
Place the soil sample in the pestle. Crush using the mortar to reduce the particle
size/increase its surface area.
Add dilute sulphuric(VI)acid to free the ions in soil sample.
Filter to separate insoluble residue from soluble filtrate
To filtrate,add three drops of aqueous ammonia as precipitating reagent. A white
precipitate of Zn(OH)2, Pb(OH)2 or Al(OH)3 is formed
Add excess aqueous ammonia to the white precipitate. If it dissolves the Zn 2+ ions are
present. Zn(OH)2 react with excess ammonia to form soluble [Zn(OH)4]2+ complex.
2.In the extraction of aluminium,the oxide is dissolved in cryolite.
(i)What is the chemical name of cryolite?
Sodium hexafloroaluminate/Na3AlF6
34
(ii)What is the purpose of cryolite?
To lower the melting point of the electrolyte/Aluminium oxide from about 2015 oC to
900oC
(iii)Name the substance used for similar purpose in the Down cell
Calcium chloride/CaCl2
(iv)An alloy of sodium and potassium is used as coolant in nuclear reactors.Explain.
Nuclear reactors generate a lot of heat energy. sodium and potassium alloy reduce/lower
the high temperature in the reactors.
(v)Aluminium metal is used to make cooking utensils in preference to other
metals.Explain.
Aluminium
(i) is a very good conductor of electricity because it has three delocalized electrons
in its metallic structure
(ii)is cheap,malleable,ductile and has high tensile strength
(iii)on exposure to fire/heat form an impervious layer that prevent it from rapid
corrosion.
3.Study the scheme below and use it to answer the questions that follow.
(a)Identify:
(i)solid residue L
Iron(III)Oxide/Fe2O3
(ii)Solid N
Aluminium hydroxide /Al(OH)3
35
(iii)Filtrate M
Sodium tetrahydroxoaluminate/ NaAl(OH)4 and sodium silicate/ NaSiO3
(iv)Solid P
Aluminium oxide/ Al2O3
(v)Gas Q
Oxygen/O2
(vi)Process K1
Filtration
(vii)Process K2
Electrolysis
(b)Write the equation for the reaction taking place in the formation of solid P from
solid N
2Al(OH)3 ->
Al2O3 (s) +
3H2O(l)
(c)Name a substance added to solid N before process Process K2 take place.
Cryolite/Sodium tetrahydroxoaluminate/ NaAl(OH)4
(d)State the effect of evolution of gas Q on
(i)process K2
Oxygen produced at the anode reacts with the carbon anode to form carbon(IV) oxide
which escape. The electrolytic process needs continuous replacement of the carbon
anode.
(ii)the environment
Oxygen produced at the anode reacts with the carbon anode to form carbon(IV) oxide
which escape to the atmosphere.CO2 is a green house gas that cause global warming.
(e)An aluminium manufacturing factory runs for 24 hours. If the total mass of
aluminium produced is 27000kg,
(i)Calculate the current used. (Faraday constant=96500Coulombs, Al=27.0).
(ii)assuming all the gas produced react with 200kg of anode ,calculate the loss in mass
of the electrode.(Molar gas volume at room temperature = 24dm3,C=12.0)
Working
Equation at Cathode
Al3+(l)
+
3e
->
Al(l)
27g Al -> 3 Faradays = 3 x 96500C
(27000kg x 1000) g -> (27000kg x 1000) g x 3 x 96500C
27g
=289500000000 Coulombs
36
Current =
Quantity of electricity =>289500000000 Coulombs
Time in seconds
24 x 60 x 60
3350690Ampheres
Working
Equation at Anode
2O2-(l)
+
4e
->
O2(g)
4 Faradays
-> 4 x 96500C24dm3 O2(g) 289500000000 Coulombs -> 289500000000 Coulombs x 24dm3
4 x 96500C
18,000,000dm3
Chemical equation at anode
O2(g) +
C (s) ->
CO2(g)
Method 1
24dm3 of O2(g)
->
18,000,000dm3 of O2(g) ->
12.0g Carbon
18,000,000dm3 x 12 = 9000000g = 9000kg
24dm3
1000g
Loss in mass of the carbon graphite anode = 9000kg
NB:Mass of the carbon graphite anode remaining =27000kg - 9000kg =18000kg
The flow chart below shows the extraction of iron metal.Use it to answer the questions
that follow.
(a)Identify:
(i)gas P
Carbon(IV)oxide/CO2
(ii)Solid Q
37
Carbon/coke/charcoal
(iii)Solid R
Carbon/coke/charcoal
(iv)Solid V
Limestone/calcium carbonate/CaCO3
(v)Solid S
Iron/Fe
(b)Write the chemical equation for the reaction for the formation of:
(i)Solid S
Fe2O3(s) + 3CO(g) -> 2Fe(s) + 3CO2(g)
(ii)Carbon(II)oxide
C(s) + CO2 (g) -> 2CO (g)
(iii)Slag
SiO2(s) + CaO(s) -> CaSiO3(s)
Al2O3 (s) + CaO(s) -> Ca Al2O4(s)
(iv)Gas P
C(s)
+ O2 (g) -> CO2 (g)
(c)State two uses of:
(i)Solid S
Iron is used in making:
(i)gates ,pipes, engine blocks, rails, charcoal iron boxes, lamp posts because it is cheap.
(ii)nails, cutlery, scissors, sinks, vats, spanners, steel rods, and railway points from steel.
Steel is an alloy of iron with carbon, and/or Vanadium, Manganese, Tungsten, Nickel
,Chromium.
It does not rust/corrode like iron.
(ii)Slag
(i) tarmacing roads
(ii) cement manufacture
(iii) as building construction material
3.You are provided with sulphuric(VI)acid ,2M aqueous ammonia and two ores
suspected to contain copper and iron. Describe with explanation how you would
differentiate the two ores.
Crush the two ores separately in using a mortar and pestle to reduce the particle
size/increase the surface area.
Add sulphuric(VI)acid to separate portion of the ore. Filter.
38
To a portion of the filtrate,add three drops of 2M aqueous ammonia then axcess
Results
A green precipitate insoluble in excess 2M aqueous ammonia confirms the ore contain
Fe2+ ion.
A brown precipitate insoluble in excess 2M aqueous ammonia confirms the ore contain
Fe3+ ion.
A blue precipitate that dissolve in excess 2M aqueous ammonia to form a deep/royal
blue solution confirms the ore contain Cu2+ ion.
4. Use the flow chart below showing the extraction of Zinc metal to answer the
questions that follow
(a)Name:
(i)two ores from which Zinc can be extracted
Calamine(ZnCO3)
Zinc blende(ZnS)
(ii)two possible identity of gas P
Sulphur(IV)oxide(SO2) from roasting Zinc blende
Carbon(IV)oxide(CO2) from decomposition of Calamine.
(b)Write a possible chemical equation taking place in the roasting chamber.
2ZnS(s)
+
3O2 (g) -> 2ZnO(s)
+ 2SO2(g)
ZnCO3(s)
->
ZnO(s)
+ CO2(g)
(c)Explain the effect of the by-product of the roating on the environment.
Sulphur (IV)oxide from roasting Zinc blende is an acidic gas that causes “acid rain” on
dissolving in rain water.
Carbon(IV)oxide(CO2) from decomposition of Calamine is a green house gas that causes
global warming.
(d)(i)Name a suitable reducing agent used in the furnace during extraction of Zinc.
Carbon(II)oxide
39
(ii)Write a chemical equation for the reduction process
ZnO(s) +
CO(g) ->
Zn(s)
+ CO2(g)
(e)(i)Before electrolysis, the products from roasting is added dilute sulphuric
(VI)acid. Write the equation for the reaction with dilute sulphuric(VI)acid.
ZnO(s) + H2SO4 (aq) -> Zn SO4(aq) + H2(g)
(ii)During the electrolysis for extraction of Zinc,state the
I. Anode used
Aluminium sheet
II. Cathode used
Lead plate coated with silver
(ii)Write the equation for the electrolysis for extraction of Zinc at the:
I.Cathode;
Zn2+(aq)
+
2e -> Zn(s)
II.Anode;
4OH-(aq) -> 2H2O(l) + O2(s) + 4e
(f)(i)What is galvanization
Dipping Iron in molten Zinc to form a thin layer of Zinc to prevent iron from rusting.
(ii)Galvanized iron sheet rust after some time. Explain
The thin layer of Zinc protect Iron from rusting through sacrificial protection. When all
the Zinc has reacted with elements of air, Iron start rusting.
(g)State two uses of Zinc other than galvanization.
Making brass(Zinc/copper alloy)
Making german silver(Zinc/copper/nickel alloy)
As casing for dry cells/battery
(h)Calculate the mass of Zinc that is produced from the reduction chamber if
6400kg of Calamine ore is fed into the roaster. Assume the process is 80% efficient
in each stage(Zn=64.0,C=12.0,O=16.0)
Molar mass ZnCO3(s)
Molar mass Zn
Molar mass ZnO
=124g
= 64g
= 80g
Chemical equation
ZnCO3(s)
->
ZnO(s)
+ CO2(g)
Method 1
124g ZnCO3
=> 80g ZnO
40
(6400kg x1000)g ZnCO3 => (6400 x1000) x 80 = 512,000,000 g of ZnO
124
100%
=> 512,000,000 g of ZnO
80%
=> 80 x 512,000,000 g
= 409600000g of ZnO
100
Chemical equation
ZnO(s)
+
CO(g) ->
Zn(s)
+ CO2(g)
80g ZnO(s)
409600000g of ZnO
=>
=>
64g Zn(s)
409600000g x 64 = 327680000 g Zn
80
100%
=> 327680000 g Zn
80%
=> 80 x 327680000 g Zn = 262144000g of Zn
100
Mass of Zinc produced = 262144000g of Zn
5.An ore is suspected to bauxite. Describe the process that can be used to confirm
the presence of aluminium in the ore.
Crush the ore to fine powder to increase surface area/reduce particle size.
Add hot concentrated sulphuric(VI)/nitric(V) acid to free the ions.
Filter. Retain the filtrate
Add excess aqueous ammonia to a sample of filtrate.
A white precipitate confirms presence of either Al3+ or Pb2+.
Add sodium sulphate,dilute sulphuric(VI)to another portion of filtrate.
No white precipitate confirms presence of Al3+
Or Add potassium iodide to another portion of filtrate.
No yellow precipitate confirms presence of Al3+
6.The flow chart below illustrate the industrial extraction of Lead metal
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(a)(i)Name the chief ore that is commonly used in this process
Galena(PbS)
(ii)Explain what take place in the roasting furnace
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